The present invention relates generally to variable valve trains of internal combustion engines and, more particularly, to actuating assemblies of variable valve trains.
Conventional internal combustion engines utilize two throttling devices, i.e., a throttle valve and the intake valves of the engine. The throttle valve is actuated by a driver depressing and/or releasing the gas pedal, and regulates the air flow to the intake valves. The engine intake valves are driven by the camshaft of the engine. The intake valves open and close at predetermined angles of camshaft rotation to allow the descending piston to draw air into the combustion chamber. The opening and closing angles of the valves and the amount of valve lift is fixed by the cam lobes of the camshaft. The valve lift profile (i.e., the curve of valve lift plotted relative to rotation of the camshaft) of a conventional engine is generally parabolic in shape.
Modern internal combustion engines may incorporate more complex and technologically advanced throttle control systems, such as, for example, electronically controlled throttle systems and intake valve throttle control systems. Electronically controlled throttle systems, in general, eliminate the mechanical link between the gas pedal and the upstream throttle by substituting an electronic sensor to communicate driver input (i.e., gas pedal position) to an engine control module. The engine control module, in turn, electronically controls the position of the upstream throttle. Intake valve throttle control systems, in general, control the flow of gas and air into and out of the cylinders of an engine by varying the timing and/or lift (i.e., the valve lift profile) of the intake valves in response to engine operating parameters, such as, for example, engine load, speed, and driver input. Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electro-mechanical configurations, generally referred to herein as variable valve mechanisms. Examples of a variable valve mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference. Generally, and as will be described more particularly hereinafter, a variable valve mechanism includes a control shaft that is rotatable by an actuator to thereby vary valve timing, duration and lift.
Despite the advanced technology used in and the reliability of modern throttle control systems, the contingency of malfunction and even failure must be considered. Malfunction and/or failure of the actuator of a variable valve mechanism results in the engine either stalling completely or, at best, continuing to run at a very low output level due to an improper air-to-fuel ratio. A variable valve mechanism having a failed actuator will be unresponsive to driver input seeking to actuate the throttle in order to increase speed or engine output. Thus, the operator of the vehicle may be unable to restart the vehicle, to xe2x80x9climp homexe2x80x9d, or to drive to the nearest repair station.
The actuator in a variable valve mechanism must be capable of providing a minimum angular rotation within a maximum period of time in order to provide appropriate response to driver input and to achieve satisfactory system performance. In order to conform to such a specification, an actuator may sacrifice resolution, i.e., the capability of making small or fine adjustments in rotational position, in the interest of rotational speed. Thus, the actuator may not be capable of making fine adjustments in the angular position of the control shaft. A variable valve mechanism having such an actuator may be incapable of finely tuning the valve lift profile. Inability to finely tune the valve lift profile can result in rough engine idle and a decrease in system and/or engine efficiency.
Therefore, what is needed in the art is an apparatus that provides a limp home capability to a variable valve mechanism.
Furthermore, what is needed in the art is an apparatus that provides driver control over a variable valve mechanism having a failed main actuator.
Moreover, what is needed in the art is an apparatus that provides the capability to finely tune and/or adjust the valve lift profile of a variable valve mechanism.
The present invention provides a variable valve actuating assembly including a secondary actuator.
The invention comprises, in one form thereof, a variable valve actuator assembly including a main actuator, a secondary actuator and an actuator shaft. The actuator shaft is coupled to each of the main actuator and the secondary actuator. The main actuator and the secondary actuator are each separately and independently selectable for rotating the actuator shaft.
An advantage of the present invention is that the secondary actuator provides for actuation of the control shaft, and thereby adjustment of the valve lift profiles, in the event of a failure of the main actuator.
Another advantage of the present invention is that the secondary actuator enables fine tuning of the valve lift profiles under engine idle conditions.
A still further advantage of the present invention is that the secondary actuator enables a driver to restart and drive a vehicle having an engine in which the main actuator has failed.